Electricity
Electric Charge
History of Electricity
 600 B.C.-Thales discovered
static electricity.
 1600 - William Gilbert names
the force electricity
 Mid 1700's - Ben Franklin
shows that lightning is made of
electricity, and does numerous
experiments
History of Electricity
 1800 - Volta makes first battery
 1878 - T. Edison creates electric light bulb
Electricity
 Electricity is a force created by a
difference in charges (+ & -) due to gained
or lost electrons.
 Electron- negatively charged particle
 Proton- positively charged particle
 Atoms usually are neutral
 When electricity is flowing between two
points, this is actually electrons moving
from point A to point B.
 This is called an electrical current.
 In order for these electrons to flow, however,
there must be a difference in charges (# of
electrons built up) between the 2 points.
 Just like heat flow needs a difference in
temperatures.
 Electricity always flows from a location with
a negative charge to a location with a
positive charge.

(like charges repel, opposites attract)
-
+
 Think of a battery, the top
has a + charge and the
bottom has a negative
charge. So when they are
connected, electrons flow
from the bottom to the top.
Static Electricity
 You may have noticed that if you walk
across the carpet in socks, and then
touch your cat’s nose, it will shock
him/her.
 This is because, you picked up some
free electrons walking over the carpet
(kind of like dust), and therefore
gained a negative charge.
 Touching kitty’s nose allows you to dissipate
that charge (send the extra electrons to an
area with fewer electrons, negative to positive)
 The shock will continue until both surfaces are
at the same charge (neutralized)
Static Electricity
 Static Electricity - the net
accumulation of electric charges on an
object, created by transferring electrons
from rubbing two objects together
 Electric Field - force exerted by an eon anything that has an electric charge
 opposite charges attract
 like charges repel
Static Electricity
 Static Discharge
 the movement of
electrons to relieve a
separation in charge
 Van der Graff Generators basically induce a
strong electrical field (can be either positive
or negative depending on the setup) into a hollow
metal sphere. This field can the release
electrons into the surrounding air when the
voltage becomes great enough.
Conductors
 Conductor
 material that allows electrons to
move through it easily
 e- are loosely held
 ex: metals like copper and silver
Insulators
 Insulator
 material that doesn’t allow electrons
to move through it easily
 e- are tightly held
 ex: plastic, wood, rubber, glass
Electroscope
 Electroscope
 instrument that
detects the presence
of electrical charges
 Gold foil leaves
separate when they
gain either a + or charge
Electricity
Electric Current
Circuit
 Circuit
 closed path through
which electrons can flow
Potential Difference
 Potential Difference (Voltage)
 difference in electrical potential
between two places
 large separation of charge creates
high voltage
 the “push” that causes e- to move
from - to +
 measured in volts (V)
Voltage Difference
 In some ways, the electric force that
causes charges to flow is similar to
the force acting on the water in a
pipe.
 Water flows from higher pressure to
lower pressure.
Current
 Current
 flow of electrons through a conductor
 depends on # of e- passing a point in
a given time
 measured in amperes (A)
Direct Current (DC)
 In most electrical circuits, the current
will flow in only 1 direction. This is
called direct current or DC.
 Examples: batteries, lightning, and
static electricity.
Alternating Current (AC)
 An alternating current will send a flow
of electrons in 1 direction through a
circuit, and then it will reverse the
flow in the other direction.
 Household outlets are an example of
AC current. They reverse the
direction of the current about 120
times per second.
Lightning
 Lightning is a form of direct current (DC)
produced by static electricity in clouds.
 The static is formed when air molecules
move past each other (just like clothes in a
dryer).
 The negative charges group at the
bottom of the cloud and transfer
electrons to the ground, which has taken
on a positive charge.
Resistance
 Resistance
 opposition the flow of electrons
 electrical energy is converted to
thermal energy & light
 measured in ohms ()
Copper - low resistance
Tungsten - high resistance
Resistance
 Resistance depends on…
 the conductor
 wire thickness
• less resistance
in thicker wires
 wire length
• less resistance in shorter wires
 temp - less resistance at low temps
Bell Ringer
 What is voltage?
 What is resistance?
 What is current?
Ohm’s Law
 Ohm’s Law
V=I×R
V
I
R
V: potential difference
(V)
I: current (A)
R: resistance ()
• Voltage increases when current increases.
• Voltage decreases when resistance increases.
Ohm’s Law
 A light bulb with a resistance of 160 
is plugged into a 120-V outlet. What is
the current flowing through the bulb?
GIVEN:
WORK:
R = 160 
V = 120 V
I=?
I=V÷R
I = (120 V) ÷ (160 )
I = 0.75 A
V
I
R
Electricity
Electrical Circuits
Circuit Components
A - Battery
B - Switch
C - Light Bulb
D - Resistor
Batteries
 To keep an electric current continually
flowing in the electric circuit- a voltage
difference needs to be maintained in
the circuit.
 A battery can provide the voltage
difference that is needed to keep
current flowing in a circuit.
 Current flows as long as there is a
closed path that connects one battery
terminal to the other battery terminal.
Types of Batteries
 Dry Cell -consists of two electrodes
surrounded by a material called an
electrolyte (moist paste).
 One electrode is the carbon rod, & other
is the zinc container.
 electrolyte is a moist paste containing
several chemicals.
Types of Batteries
 Wet Cell - contains two connected
plates made of different metals or
metallic compounds in a conducting
solution.
 A wet-cell battery contains several
wet cells connected together.
Series Circuits
 Series Circuit
 current travels in a single path
• one break stops the flow of current
 current is the same throughout circuit
• lights are equal brightness
 each device receives a fraction of the
total voltage
• get dimmer as lights are added
Parallel Circuits
 Parallel Circuits
 current travels in multiple paths
• one break doesn’t stop flow
 current varies in different branches
• takes path of least resistance
• “bigger” light would be dimmer
 each device receives the total voltage
• no change when lights are added
Household Circuits
 The wiring in a house must allow for
the individual use of various
appliances and fixtures.
 This wiring is mostly a combination of
parallel circuits connected in an
organized and logical network.
 The main switch and circuit breaker
or fuse box serve as an electrical
headquarters for your home.
Household Circuits
 Parallel circuits branch out from the
breaker or fuse box to wall sockets,
major appliances, and lights
 To protect against overheating of the
wires, all household circuits contain
either a fuse or a circuit breaker.
Fuses
 An electrical fuse contains a small
piece of metal that melts if the current
becomes too high.
 When it melts, it causes a break in
the circuit, stopping the flow of
current through the overloaded
circuit.
 To enable current to flow again in the
circuit, you must replace the blown
fuse with a new one.
Circuit Breakers
 A circuit breaker contains a
bimetallic strip that bends when the
current in it is so large that it gets hot.
 The bending causes a switch to flip
and open the circuit, stopping the
flow of current.
 Circuit breakers usually can be reset
by pushing the switch to its "on"
position.
Electricity
Measuring Electricity
Electrical Power
E
P t
 Electrical Power
 rate at which electrical energy is
converted to another form of energy
P: power (W)
P=I×V
I: current (A)
V: potential
difference (V)
Electrical Power
 A calculator has a 0.01-A current flowing
through it. It operates with a potential
difference of 9 V. How much power does it
use?
GIVEN:
WORK:
I = 0.01 A
V=9V
P=?
P=I·V
P = (0.01 A) (9 V)
P = 0.09 W
P
I
V
Electrical Energy
E
P t
 Electrical Energy
 energy use of an appliance depends
on power required and time used
E: energy (kWh)
E=P×t
P: power (kW)
t: time (h)
Electrical Energy
 A refrigerator is a major user of electrical
power. If it uses 700 W and runs 10 hours
each day, how much energy (in kWh) is
used in one day?
GIVEN:
WORK:
P = 700 W = 0.7 kW E = P · t
t = 10 h
E = (0.7 kW) (10 h)
E=?
E = 7 kWh
E
P t
Magnetism
Characteristics of Magnets
Magnetism
Magnetism
 force of attraction or repulsion
between unlike or like poles
 due to the arrangement of electrons
 closely related to electricity
Magnetic Poles
 Magnetic Poles
 like poles repel
 unlike poles attract
 a broken magnet creates new poles
Magnetic Field
 Magnetic Field
 area around a magnet where magnetic
forces act
 field lines show direction of field (NS)
Magnetic Domain
 Magnetic Domain
 groups of atoms with aligned magnetic
poles
domain
 in a magnetized object, domains are all
aligned
Magnetism
Uses of Magnetic Fields
Electromagnet
 Electromagnet
 strong, temporary magnet formed when
current is passed through a coil of wire
surrounding an iron core
 Electromagnets have 2 advantages over
normal magnets:
1. They can be turned on and off.
2. Their strength can vary based on the amount
of current flowing.
 Examples of electromagnets include cranes
in scrap yards, telegraphs, and certain
types of doorbells.
Electromagnetic Induction
 Electromagnetic Induction - producing a
current by moving a wire through a magnetic field
 some microphones
work just like minispeakers in reverse
 sound waves cause
coil to move  current
Coil
Dynamic Microphone
Electric Motors
 Electric motors are devices which convert
electricity to mechanical energy.
 Most household appliance are examples of
electric motors.
Ex.: washing machine, fan, refrigerator,
VCR, dishwasher, hair dryer, etc.
Motor
 Motor
 electrical energy  mechanical energy
 electromagnet
rotates between
the poles of a fixed
magnet
 commutator
reverses the poles
of the e’magnet
Electric Generator
 Electric Generator
 mechanical energy  electrical energy
 armature is
rotated between
magnet poles
 magnetic field
induces a
current in the
wire coil
MOTOR
GENERATOR
Electric Generators
 The electricity supplied to
your home is produced by an
electric generator. This is a
device which changes
mechanical (kinetic) energy
into electricity.
 Most electric power which is
generated in Missouri is
either from hydroelectric or
fossil fuel power plants.
Electric Generator
 Hydroelectric Dam
 PE of lake water is
converted to KE
 mechanical KE
turns the generator
shaft which creates
electrical energy
Speaker
 Speaker
 electrical energy  mechanical energy
 wire coil moves back &
forth as its magnetic
field interacts with the
field of a fixed magnet
 forced vibration causes
the cone to move 
sound
Transformer
 Transformer
 increases or decreases AC voltage
 primary coil AC produces a magnetic field that
induces AC in the secondary coil
 voltage ratio = ratio of turns in each coil
Transformer
 Step-up Transformer
 increases the voltage
 more turns
 power plants
Step-down Transformer
 decreases the voltage
 fewer turns
 household appliances
(hairdryers, etc.)
Transformers
 The AC which comes from your
household outlets usually has a voltage of
about 120V.
 The voltage of the power lines outside,
however, is much higher. Before entering
your house, the electricity from the power
lines must pass through a transformer.
This is a device which can increase or
decrease the voltage which exists
between 2 points.
 Transformers outside your house make the
voltage in your outlets safe for household
appliances.
 Occasionally a lightning strike make take out a
transformer, and send a power surge into your
house.